1. Field of the Invention
The present invention relates to systems for returning various asbestos-cement plant effluents for use in the production of and incorporation directly into the asbestos-cement products of said production plant. Such asbestos-cement products may include pipe of various sizes, sheet and sheet-like products such as panels, and shingles with or without decorative surface treatment. Such products are generally produced from an aqueous slurry which may include various types of asbestos fibers, cellulose fibers, a source of silica such as silica sand, diatomaceous earth, or a silica flour, a cement material such as portland cement, and/or similar materials. In the production of these materials large quantities of water containing a fraction of these solid materials and certain minor percentages of additives is generated. Also, when these machines are not producing such products, they must be thoroughly cleaned lest the solid products coalesce in the various parts of these machines, making them relatively unusable. This cleaning and machine shutdown for felt changes and for weekends produces further large amounts of water containing widely varying fractions of these asbestos-cement solids and additives.
2. Description of the Prior Art
In general, attempts to return or recycle effluents from the various product making machinery in an asbestos-cement plant has been limited to the return of clarified or generally clear water. In such a system, plant effluents containing varying percentages of the asbestos-cement solids are collected in large tanks or pools. Here the solids are permitted to settle to the bottom of the tank or pool, and the relatively clear water is returned to the production machinery and added to the asbestos-cement slurry in amounts as needed, or the clarified effluent water is used to clean out the various machinery when such machinery is shut down.
The solids, having settled out, are disposed in either one of two ways. The first of these methods requires at least two very large settling tanks or pools. These tanks or pools would perhaps be more accurately described as ponds of 250 to 400 feet in length and width. Plant effluent is permitted to flow into one of these ponds. The excess of clarified water, that is water that has not evaporated from the pond and is of the proper cleanliness, is returned to the production plant for whatever uses to which it may be put. The solids, on the other hand, are allowed to accumulate in this pond until such accumulation substantially fills the pond. At this point the plant effluent is shifted to flow into the other of the two ponds since the first pond is filled with plant effluent solids, is substantially useless for further effluent clarification. The remaining water in this first pond is allowed to evaporate. This permits heavy machinery to be moved into the pond in order to break up the accreted solids and remove them to a land fill remote from the plant. Alternatively, the pond is covered with fill dirt, thus becoming a relatively useless piece of real estate. The second of the prior art methods of disposing of the solids consists of returning the relatively concentrated solid effluent from the settling tank or pond to a drying drum. The drying drum consists of a porous belt passing through a vat of the effluent slurry. This slurry passes through the belt arranged over the drum such that the solids are filtered out. The drum containing the precipitated solids is scraped to deposit the solids in the form of wet mud into waiting dump trucks to be subsequently transported to a land fill disposal.
Both of the above outlined prior art disposal methods result in a huge solids waste disposal problem. Presuming a production facility has an output of approximately 100,000 tons of asbestos-cement products per year, it is not unusual for 3,000 to 4,000 tons of waste solids per year to be disposed of by one of these two methods.